1. Field of the Invention
The present invention relates to pneumatic control valves, and, more particularly, to valves for directing motive fluid.
2. Description of the Related Art
Pneumatic control valves are mechanical devices used to provide directional control of pressurized air wherein the pressure and/or the velocity of the air is used as a motive force.
Pneumatic control valves are characterized by an electric motor or pneumatically driven piston coupled slidably or rotationally to a valve subassembly. As the motor or piston causes valve subassembly components to slide or rotate, internal air passageways are opened, closed or connected to other passageways such that pressurized air supplied to the control valve is blocked, passed thru or directed to one of multiple outlet passageways.
One use of a pneumatic control valve is to control flow of air to a turbine starter on a gas turbine or jet engine. In such a usage, when the airflow is allowed to pass thru the control valve, it causes the turbine starter to rotate. The turbine starter, in turn, is directly coupled to the jet engine and provides initial rotation of the jet engine during the start sequence. In the prior art, the pneumatic control valve may have included a flat round butterfly style shutter in the air passageway that would rotate perpendicular to the passageway axis to close and block the passage or rotate to a position parallel to the air passageway axis to open and to allow air to pass thru.
In this prior art, the butterfly valve shutter is always in the middle of the air passageway whether it is open or closed. Due to its location in the middle of the air passageway, the butterfly shutter can impede the free flow of air and result in flow turbulence or losses in pressure and flow velocity due to the obstruction of the air passageway by the butterfly shutter.
What is needed in the art therefore, is a fluid control valve for motive fluid that offers minimal restriction to flow in the open position.